Newborns spend a large portion of their time asleep. During the first postnatal month--a time when numerous cardiorespiratory changes are occurring--lambs spend about 45% of their time in quiet sleep and about 10% of their time in active sleep. Very little is known about the influence of sleep on baseline cardiorespiratory regulation or of the reflex cardiorespiratory response(s) to perturbation in young animals. I propose to do experiments to investigate: 1) the effects of sleep on baseline cardiorespiratory regulation during postnatal development, 2) the effects of sleep on cardiorespiratory regulation following sino-aortic denervation during postnatal development, 3) the effects of sleep on the cardiorespiratory response to perturbation (i.e., upper airway obstruction) before and after sino-aortic denervation during postnatal development, 4) the effects of environmental temperature on baseline cardiorespiratory regulation and the response to perturbation in sleep before and after sino-aortic denervation, and 5) the effects of sleep fragmentation on baseline cardiorespiratory regulation and the response to perturbation in sleep before and after sino-aortic denervation. The proposed studies will provide important information about the cardiovascular and the respiratory systems during sleep and may provide insight into the pathophysiology of some events such as intracranial hemorrhage and sudden infant death.